Method of producing controlled length metal filaments

ABSTRACT

Streams of molten metal are converted into solidified metal filaments having point generatrix cross-sectional shapes by directing the stream into grooves formed into a moving chillblock surface. The grooves are shaped to form a mold of one surface of the point-generatrix shape and extend substantially in the direction of movement in the chill-block surface. The movement of the chill block is disposed to effect ejection of the solidified molten stream from the groove in the form of filaments by centrifugal force.

United States Patent 1191 Mobley et al. 1 Jan. 16, 1973 54 METHOD OF PRODUCING 989,075 4/1911 Staples ..l8/2.6 ux CONTROLLED LENGTH METAL 1,063,895 6/1913 Staples ..,.l8/2.6 ux 2.0l8,478 l0/l935 Whittier ..l8/2.6 X FILAMENTS 2,206,930 7/1940 Webster ....l64/278 X [75] Inventors: Carroll E. Mobley, Columbus; 2,664,605 1/1954 Besle 6 X Robe" Mating", Worthington, 2,825,108 3/1958 Pond ..l8/2.6 x both of Ohio 1 2,886,866 5/1959 Wade ..l64/278 X [73] Assignee: The Battelle Development Corpora- Primary ExaminerR. Spencer Annear tion, Columbus, Ohio Attorney-Gray, Mase & Dunson [22] Filed: Dec. 28, 1970 ABSTRACT [211 App! 101399 Streams of molten metal are converted into solidified metal filaments having point generatrix cross-sectional [52] US. Cl. ..l64/78, 164/87, 264/8 Shapes y directing the Stream into grO ve formed 51 1111. c1. .3220 11/06 into a moving chill-block Surface The grooves are [58] Field of Search ..l64/82, s4, s7, 78, 276, 27s; shaped to form a mold of one Surface of the P 264/8 176 F generatrix shape and extend substantially in the direction of movement in the chill-block surface. The [56] References Cited movement of the chill block is disposed to effect ejection of the solidified molten stream from the groove in UMTED STATES PATENTS the form of filaments by centrifugal force.

112,054 2/1871 Lang ..l64/276 X 5 Claims, 9 Drawing Figures PATENTEUJAN 16 I975 3 710 842 sum 1 OF 3 Fig. 4

PATENTEDJAN 16 I975 8.710.842

SHEEI 3 [1F 3 IOOQ- g CONTINUOUS DISCONTINUOUS FLAKE g FILAMENTS FILAMENTS POWDER U E DECREASING LENGTH 2 w 3 z 25o X 2 I25- r- O t v I F 0 I00 200 300 400 500 I000 IMPINGEMENT VELOCITY m FT./SEC.

EJECTION VELOCITY F|g 8 PRIOR ART 0) 2 g FLAKE mscommuous commuous 9 POWDER FILAMENTS FILAMENTS 2 5 DECREASING -l ENGTH (I) U) 2 x 250- U 5 |25- I I I I l I I00 200 300 400 500 600 M 1000 EJECTION VELOCITY IN FTJSEC.

IMPINGEMENT VELOCITY 9 PRIOR ART METHOD OF PRODUCING CONTROLLED LENGTH METAL FILAMENTS BACKGROUND hot and cold working procedures and subsequent draw- 1 ing, heat-treating, and surface-conditioning steps required for the production of thin-gage wire require capital equipment investments and labor costs that prohibit all but the large, established metal industries from producing such products. Further, the resultant product though high in quality is prohibitively expensive for many applications.

One significant need for a cheap source of relatively high-strength fine wire relates to the discovery that the addition of fine wire or filaments to concrete aggregates provides a high-strength crack-resistant material not heretofore known. It has been estimated that highway surfaces constructed of such material will resist wear and the stress of weather many times that of presently known road surfacing materials. However, wire filaments made by any presently known manufacturing means raises the cost of such road surfacing aggregates to a point where they are priced out of the market.

One method for making wire in the form of thin-gage filaments directly from molten metal is known as the metal-spin process and involves pressure casting of a thin stream of molten metal onto the smooth surface of a rotating dish or saucer-shaped chill block. The speed of rotation of the chill-block surface and the speed of the molten metal stream are such that the molten metal solidifies on the chill-block surface and-is ejected from the chill-block surface in solid form by the centrifugal forces imposed by rotation. This method is fully described by US. Pat. No. 2,825,108 to Robert B. Pond.

The filaments made by the method of the Pond patent are generally rectangular in cross section and may reach in thickness from about 1,000 microns to about 0 (rarely less than 1 micron) and in width from about 6,000 microns to about 2 microns. Attempts to produce greater thickness fibers generally result in excessive attenuation of the molten stream either before or after impringement on the rotating chill block resulting in low production yields of the desired fiber.

Such filaments may also be produced by impinging the molten stream onto a chill-block surface that consists of the polished surface of a rotating cylinder or drum. The molten stream solidifies and is ejected from the chill-block surface after appropriate solidification (dwell time on the chill-block surface) by the centrifugal forces imposed by a rotating drum in a manner that corresponds to that described in the patent to Pond (US. Pat. No. 2,825,108).

A still further method for making melt-spin type continuous filaments involves the utilization of a chillblock surface that consists of a continuous belt. Such continuous belt will preferably be constructed of a resilient metal so as to exhibit a polished metal surface. The parameters of molten stream speed, chill-block surface speed etc. are substantially identical to those described by the aforementioned Pond patent in conjunction with the rotating saucer-shaped chill block with the exception, of course, the impingement surface is substantially flat rather than being concave as in the Pond system.

The Pond US. Pat. Nos. (2,886,866; 2,899,728; 2,904,859; and 2,910,744 as well as 2,825,108 mentioned above) constitute an improvement over the methods of utilizing rotating cylinders and endless belts. However, for some applications the latter procedures may be readily employed.

Although filaments made by the above-described Pond process are satisfactory for many applications including concrete reinforcement, we have found a method for making such filaments with a pointgeneratrix cross-sectional shape (L,C, U,Z,W, etc.). We have found that the point-generatrix shape provides a higher-section modulus or greater stiffness and resistance to bend for a given volume of filaments. Accordingly, such filaments offer greater reinforcement characteristics than has heretofore been known for melt-spin type fibers or filaments.

THE INVENTION We have found that in the art of producing metal filaments by impinging a stream of molten metal onto the surface of a rotating chill block, that contrary to prior art teachings, re-entrance to sharp angles may be provided on the surface of the chill block in the form of grooves on the surface of the rotating saucer-shaped chill block to shape the molten metal filament as it is cast onto the moving chill-block surface.

The surface smoothness of the chill block must remain the same as that taught by the Pond patents, that is, the finish of the groove surface must be smooth and will preferably have a surface finish of from less than 1 micro inch to approximately 40 micro inches. However, the shaped surface itself may deviate beyond the thickness within the width of the filament being produced (as required by Pond) so long as the deviation extends in the direction of movement of the spindisk surface.

However, the surface finish itself cannot be coarser than the thickness of the filament to be produced. For example, where the groove is in the form of a V, the thickness of the filaments may be less than the length of either leg of the V-shape but the surface within the groove forming the V-shape must be at least as smooth as the thickness of the filament being produced.

We find that although point-generatrix-shaped filaments produced in the manner described above while utilizing dish-or convex-chill blocks, exhibit a desired, improved high-sectional modulus over nonshaped (i.e., rectangular) filaments, the preferred embodiments of our invention involve the utilization of grooved rotating cylinders or drum-shaped chill blocks or grooved endless belts. The reason for this is that the centrifugal force influence of the rotating disk or saucer on the filaments being cast imparts an undesirable torque or bend on the product.

Such filaments are not as satisfactory as straight filaments for many applications including concrete reinforcement. The product made from casting onto. a rotating-cylinder or endless-belt-type chill block possesses a less offensive torque or bend than the product made from casting onto a spinning-disk-type chill block.

Additionally, where continually casting endless filament as opposed to short lengths, material with a torque or downward bend such as is obtained from a rotating-cylinder type of chill block or endless-belt type of chill block may be readily wound on spools for easy handling and shipment while that coming off a rotating chill block of the dish or saucer type possesses a bend or torque that resists winding on a spool or spindle.

A still further advantage of utilizing the cylinder or endless-belt type chill block relates to the fact that sideby-side grooves may be cut into such chill blocks that will have equal length and casting characteristics so that parallel molten metal streams of equal speed and volume may be utilized in the production of multiple filaments, while circumferential grooves cut in a rotating disk or saucer will vary in speed thus varying the other parameters involved and complicating multiple melt spinning from a single chill block.

The surface of the rotating cylinder chill block must meet all of the parameters of the rotating disk of the aforementioned Pond patent (i.e., surface finish and chill characteristics). Further, the relative surface speed of the chill block to the speed of the fluid molten stream must be the same. The diameter of the cylinder or drum is not particularly critical although it is unlikely one would use a cylinder or drum of less than about 1 inch diameter or more than about 3 feet. The grooves, of course, must be circumferential and, as stated above, the surface must be polished.

The parameters of utilizing an endless belt must also equate those of the spinning disk or dish of the Pond patent insofar as chill block characteristics and surface smoothness are concerned. The groove must come, of course, parallel to the belt. One potential difference is dwell time. The molten metal stream must contact the belt sufficiently near the end of the belt for the centrifugal forces of the belt to throw off the filaments as it rounds its pulley.

Some applications for wire filaments, particularly where they are used for reinforcement purposes, require that the wire be subdivided into short lengths ranging from about one-sixteenth inch to about three to eight inches. Continuously cast filament may be cut into short lengths by chopping techniques or other mechanical means. Additionally, the speed of rotation of the chill block or the speed of metal flow may be altered sufficiently to cause appropriate attenuation of the molten stream.

Mechanical chopping or subdividing of continuous filaments increases its cost, thus detracting from the overall process. It is difficult to obtain uniform length filament segments using the stream and chill block speed variables.

We have now discovered that in conjunction with our process and apparatus that we can effect accurate subdivision of filaments coming off of the chill block by including substantially transverse (to the direction of travel) grooves or mounds on the disk, cylinder, or endless belt. Such grooves or mounds cut across the surface into which the molten stream is cast to effect subdivision of the filament. Since these grooves or mounds may be accurately spaced on the disk, cylinder, or endless belt, the segmentation may be closely controlled. The transverse grooves will be deeper than the elongated grooves preferably an amount greater than the thickness of the filament being cast. If a mound, it will be at least higher (relative to the chill block surface) than the bottom of the elongated groove and preferably at least higher than the thickness of the filament being cast. Such groove or mound, of course, need be no longer than the width of the elongated groove or the filament being cast. Where the sub-v stantially transverse groove or mound is used to attenuate rectangular filaments cast onto nonelongated grooved but smooth surfaced chill block, they will preferably extend above or below the chill block surface an amount that exceeds the thickness of the filament being cast.

IN THE DRAWINGS FIG. 1 is a fragmented perspective view of molten metal being extruded into a stream that is directed onto a rotating disk formed with a groove in accordance with the present invention;

FIG. 2 is a fragmented cross-sectional view of a portion of the disk of FIG. 1 showing a cross-sectional view of the filament being cast;

FIG. 3 is a fragmented perspective view of molten metal being extruded into a stream onto a rotating cylinder formed with a groove in accordance with the present invention;

FIG. 4 is a cross-sectional fragment of the drum of FIG. 3 showing the groove and the filament being cast;

FIG. 5 is a fragmented perspective view of molten metal being extruded onto a moving, endless belt formed with grooves in accordance with the present invention;

FIG. 6 is a fragmented perspective view of a rotating chill block similar to the embodiment of FIG. 3 showing transverse grooves disposed to subdivide the cast molten filament into segments;

FIG. 7 is a perspective view of a rotating chill block similar to the embodiment of FIG. 1 showing transverse grooves disposed to subdivide the filament;

FIG. 8 is a graph showing a variation of filament thickness and length with velocity; and

FIG. 9 is a graph showing variation of filament thickness and length with ejection velocity.

In the embodiment of FIG. 1 molten metal stream 10 extruded from the nozzle 12 impinges on the polished surface of rotating dish or disk-shaped chill block 14 for a dwell time represented by the area 16 whereupon it is ejected from the disk as at 18 as a substantially solidified metal filament. Chill block 14 is provided with a raised portion 20 (see FIG. 2) forming a shoulder 22 which creates a groove into which the molten stream 10 is directed. Note that stream 10 upon lodging into shoulder 22 acquires a point generatrix shape in the form of an L or V cross section. As in U.S.

' Pat. No. 2,825,108, the surface tension of the filament of molten stream 18 is reduced upon solidification and the filament 18 is thrown from the block or disk 14 in the manner shown by FIG. 1. Note that this filament solidifies when the filament is semicircular in shape and is then cast from the chill block in the shape represented by the arrow 24. Obviously, such torque or bent shape remains in the filament reducing its attractiveness for many applications.

The bent filament problem is somewhat alleviated by the embodiment of FIGS. 3 and 4 where the cast molten stream 30 is directed to a groove 42 formed circumferentially in the polished surface of the cylindershaped chill block 34. The molten metal solidifies within the dwell time 36 forming a V or L-shaped point-generatrix member 38 (see FIG. 4) as it is cast by centrifugal forces from the groove 42. Since the filament 38 is bent in the manner shown by the arrow 44, it is more readily wound upon spools and may be more readily straightened for reinforcement use. Such torque or bent shape is preferred over that of the product of the embodiment of FIGS. 1 and 2.

In the embodiment of FIG. 5 a plurality of molten streams 50 are shown to be cast into a plurality of grooves 62 formed in the surface of the endless belt chill block 54. After dwell time 56, the solidified V or L-shaped filaments 58 are centrifugally expelled from the groove 62 as the belt turns on rollers 63.

It should be noted that filaments 58 will have substantially less bend or torque since during the period of solidification or swell time 56 the filaments were relatively flatly aligned and were expelled from the belt only upon its turning on rollers 63.

The illustrative embodiments of FIGS. 7 and 6 correspond to the embodiment of FIGS. 1 and 3 with the exception that there is provided transverse grooves 17 and 37 (transverse to the direction of motion of the surface of the respective chill blocks) that cut across or bisect the forming grooves 22 and 42, respectively. The grooves 17 and 19 are preferably deeper than the grooves 22 and 42 and are spaced so as to cause the molten streams to attenuate prior to complete solidification and yield segments or short filaments 23 and 43, respectively. Obviously, spacing grooves 17 and 19 may be gaged to provide any desired length segments of filaments 23 and 43. In the embodiment of FIG. 5 dotted lines 61 illustrate where transverse grooves could be cut to provide segmented filaments while employing the endless belt chill block concept in lieu of the rotating cylinder or drum of FIG. 3 or the spinning disk of FIG. 1.

The transverse grooves 37 of FIG. 7, 17 of FIG. 6, and 61 of FIG. 5 may be formed into the surface of a chill block disk cylinder or endless belt that is not provided with grooves 22, 42, or 62 so that the product may be that of U.S. Pat. No. 2,825,108, Pond, which consists of flat or rectangular-shaped filaments that are cast onto the surface of the smooth rotating disk, drum, or belt to provide the desired length segments equivalent to that of segments 43 and 23.

It should be noted that the transverse grooves may be mounds or elevations rather than grooves to effect the same result. Such grooves or mounds will preferably exceed the thickness of the filaments being cast in depth or heighth.

It will, of course, be understood that the nozzles 12 used to eject or create a stream of molten metal such as streams 10, 30, and 50 of FIGS. 1, 3, and 5, respectively, may advantageously be the extrusion device of FIGS. 1 and 2 of U.S. Pat. No. 2,825,108, Pond. However, it is to be understood that these streams may be created by other means including pouring from a ladle for a distance wherein the desired acceleration parameters are obtained.

The variables or parameters to the present invention as has been stated above as they relate to temperature of the molten metal, the velocity of ejection, and the size of the ejection orifice are correlated with the surface speed of the chill block at the point of impingement of molten metal to cast filament of various thicknesses, widths, and lengths and by altering one or more of the variables in the casting process. Variation in the dimensions maybe readily accomplished in a manner substantially identical to that disclosed by U.S. Pat. No. 2,825,108, Pond. Generally, the higher the temperature of the molten metal and the slower the ejection velocity thereof, with a given size orifice and mold surface speed, the thinner the filaments will be. With all the other variables held constant, the closer the velocity of ejection approaches that of surface speed at the point of impingement, the greater the continuity of the produced filament. Also, with all other variables held constant, the larger the orifice size, the wider (overall width) the filament will be.

The data of FIGS. 8 and 9 correspond precisely with that of U.S. Pat. No. 2,825,108. With respect to FIG. 8, if the ejection velocity is maintained at about feet per second (orifice size, temperature of metal, and type of metal or alloy being constant), there will be continuous filaments ranging in thickness from 1,000 microns down to just above zero as the impingement velocity is increased from, say 50 to 400 feet per second. The same parameters apply to the method of the present invention as it relates to the thickness of the pointgeneratrix shape filament. Thereafter, there will be discontinuous filaments with a progressive decrease in length until the flake powder stage is reached well before an impingement velocity of 1,000 feet per second is reached.

As seen in FIG. 9 with an impingement velocity maintained at 600 feet per second and with orifice size temperature of metal and type of metal or alloy being constant, there will be flake powder with ejection of velocity ranging from zero to a little over 200 feet per second discontinuous filaments will be evident before 300 and these increases in length until, when the ejection velocity reaches about 600 per second, continuous filaments result.

The minimum thickness figures indicated by the dark lines in FIGS. 8 and 9 is about 1.0 micron. These graphs show tendency curves. It will be appreciated that the shape of the curves and their positions relative to the abscissa and ordinate will vary as the metal or alloy is varied, or as the orifice size or temperature of the specific metal changes, or as the relative ejection and impingement velocities change. The figuresdo, however, illustrate the extent of control possible. The precision of control is, of course, no better than the precision of control of all of the variables.

In carrying out the process of the present invention, it is preferred that the relative velocity of the molten stream in the direction of motion of the surface of the moving chill block at the point of impingement (see arrow A of FIGS. 1 and 3) should be no less than about one-fifth of the velocity of the chill block surface and no more than about twice the velocity of the chill block. Under these conditions the parameters of impingement velocity and ejection velocity will obtain a more consistent filament, particularly where striving for continuous filaments in meeting the parameters set forth in FIGS. 8 and 9.

As set forth in US. Pat. No. 2,825,108, the angle of incidence which the stream of molten metal forms with the surface of the chill block may be varied with no apparent effect on the filament (where the other parameters relating to impingement and ejection velocity or relative velocity of the metal stream to the surface of the chill block are met). However, it is preferred that the angle of incidence be within the range of from about 30 to 90 with a molten stream having a velocity in the direction of motion of the chill block surface. Optimum results are obtained at an angle of about 60.

For the purpose of the present specification and claims, the term point-generatrix shape shall mean any cross-sectional shape traceable by a point (such as the point of a pencil) to create a continuous cross-sectional shape without crossing lines or retracing a-single line (i.e., C,L,V,U,Z, N,W, etc.). Such shapes may be created by forming a groove in the moving chill block having a surface contour that corresponds to one side of the point-generatrix shape so that such shape may be created by casting a film of molten metal onto the surface of the groove which when solidified and cast from the the surface by centrifugal forces constitutes a filam'ent having a cross section that corresponds to the point-generatrix shape.

The following specific examples are illustrative only and in no way limit the scope of the present specification or claims but positively demonstrate the operability of some embodiments and render the operability of others obvious.

EXAMPLE 1 A mil diameter stream of molten zinc extruded from a nozzle and traveling at approximately 350 centimeters per second was directed onto a rotating, conical disk-type aluminum chill block containing a single radial step (see FIG. 1). The stream was directed at an included angle to the surface of the spinning disk at about 60. The impingement (i.e., tangential velocity at the step apex was about 2,700 centimeters per second). A continuous zinc V angle fiber approximately 1 mil thick, mils wide on each flange or section with included angle of about 90 was produced.

EXAMPLE 2 A 20 mil diameter stream of molten cast iron traveling at approximately 350 centimeters per second was directed onto a conical, disk-type chromium plated copper chill block containing a single radial step (see FIG. I). The stream was directed onto the surface of the chill block at an included angle of about 60. The impingement (i.e., tangential) velocity at the step apex was approximately 2,700 centimeters per second. A continuous cast iron V angle fiber approximately 1.5 mils thick and 60 mils wide on each section or flange with an included angle of about 100 was produced.

EXAMPLE 3 A molten stream of cast iron (superheated 50 to 100) ejected from a 20 mil orifice under an ejection pressure of about 20 psi (approximate stream velocity 20 feet per second) was directed onto the surface of a rotating 4-inch diameter cylinder chill block formed with a V-sha ed circumferential groove. The molten stream was irected into the groove. The chill block was constructed of copper and was chromium plated. The chill block surface velocity in the same general direction as the molten stream was feet per second (i.e., a 4-inch diameter cylinder rotating at approximately 5,000 rpm). A continuous V-shaped filament of 2 mils thickness and 20-30mils wide in segments of l-l2 inches long were produced. Yields were in the order of percent.

1 claim:

1. In the method of melt spinning or casting metal filaments wherein a stream of molten metal is impinged on a moving chill-block surface and is ejected from said surface by centrifugal force in the form of a metal filament, the improvement of providing a groove or mound in the surface of said chill block that is substantially transverse to said molten metal stream so as to attenuate said stream into segmented filaments.

2. ln the method of melt spinning or casting metal filaments wherein a stream of molten metal is impinged on a moving chill block surface and is ejected from said surface by centrifugal forces in the form of a metal filament, the improvement of providing the chill block surface with a groove elongated in the direction of movement of said chill block surface said groove being provided with at least one substantially transverse groove that bisects and crosses said elongated groove and which is deeper than said elongated groove so as to cause the cast metal to attentuate into segments before being ejected from said surface.

3. The method of claim 2 wherein said substantially transverse groove is deeper than said elongated groove in an amount exceeding the thickness of the filament being cast.

4. In the method of melt spinning or casting metal filaments where a stream of molten metal is impinged on a moving chill block surface and is ejected from said surface by centrifugal forces in the form of a metal fila ment, the improvement of providing the chill block surface with a groove elongated in the direction of movement of said chill block surface said groove being provided with at least one substantially transverse mound higher than the bottom of said elongated groove in an amount exceeding the thickness of the filament being cast.

5. In the method of melt spinning or casting metal filaments wherein a stream of molten metal is impinged on a moving chill-block surface and is ejected from said surface by centrifugal forces in the form of a metal filament the improvement of providing a chill-block surface consisting of the flat surface of an endless belt having grooves in the direction of movement with the solidification of the metal being affected at a rate ranging from approximately 50 to 1,000 feet per second. 

1. In the method of melt spinning or casting metal filaments wherein a stream of molten metal is impinged on a moving chillblock surface and is ejected from said surface by centrifugal force in the form of a metal filament, the improvement of providing a groove or mound in the surface of said chill block that is substantially transverse to said molten metal stream so as to attenuate said stream into segmented filaments.
 2. In the method of melt spinning or casting metal filaments wherein a stream of molten metal is impinged on a moving chill block surface and is ejected from said surface by centrifugal forces in the form of a metal filament, the improvement of providing the chill block surface with a groove elongated in the direction of movement of said chill block surface said groove being provided with at least one substantially transverse groove that bisects and crosses said elongated groove and which is deeper than said elongated groove so as to cause the cast metal to attentuate into segments before being ejected from said surface.
 3. The method of claim 2 wherein said substantially transverse groove is deeper than said elongated groove in an amount exceeding the thickness of the filament being cast.
 4. In the method of melt spinning or casting metal filaments where a stream of molten metal is impinged on a moving chill block surface and is ejected from said surface by centrifugal forces in the form of a metal filament, the improvement of providing the chill block surface with a groove elongated in the direction of movement of said chill block surface said groove being provided with at least one substantially transverse mound higher than the bottom of said elongated groove in an amount exceeding the thickness of the filament being cast.
 5. In the method of melt spinning or casting metal filaments wherein a stream of molten metal is impinged on a moving chill-block surface and is ejected from said surface by centrifugal forces in the form of a metal filament the improvement of providing a chill-block surface consisting of the flat surface of an endless belt having grooves in the direction of movement with the solidification of the metal being affected at a rate ranging from approximately 50 to 1,000 feet per second. 